U.S. patent number 10,239,904 [Application Number 15/292,079] was granted by the patent office on 2019-03-26 for method for producing solid lignin.
This patent grant is currently assigned to VALMET TECHNOLOGIES OY. The grantee listed for this patent is Valmet Technologies Oy. Invention is credited to Eric Enqvist, Anders Littorin, Ville Tarvo, Panu Tikka, Henrik Wallmo, Tobias Wittmann.
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United States Patent |
10,239,904 |
Enqvist , et al. |
March 26, 2019 |
Method for producing solid lignin
Abstract
Lignin-rich starting material is suspended in a first medium,
which is acidic and aqueous, to form a aqueous acidic suspension,
which is heated and allowed to form two continuous phases, a
thermoplastic lignin phase and an aqueous phase. The thermoplastic
lignin phase is separated from the aqueous phase and passed through
a shape giving process into a second medium which is at a
temperature lower than that of the thermoplastic lignin phase and
in which the thermoplastic lignin phase is essentially insoluble.
Solid lignin formed in the second medium is recovered.
Inventors: |
Enqvist; Eric (Helsinki,
FI), Tarvo; Ville (Espoo, FI), Tikka;
Panu (Espoo, FI), Wittmann; Tobias (Berlin,
DE), Wallmo; Henrik (Alingsas, SE),
Littorin; Anders (Hisings Karra, SE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Valmet Technologies Oy |
Espoo |
N/A |
FI |
|
|
Assignee: |
VALMET TECHNOLOGIES OY (Espoo,
FI)
|
Family
ID: |
57083228 |
Appl.
No.: |
15/292,079 |
Filed: |
October 12, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170101430 A1 |
Apr 13, 2017 |
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Foreign Application Priority Data
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Oct 13, 2015 [FI] |
|
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20155728 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C07G
1/00 (20130101); C08H 6/00 (20130101) |
Current International
Class: |
C07G
1/00 (20110101); C08H 7/00 (20110101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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20126030 |
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Oct 2012 |
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FI |
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2006031175 |
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Mar 2006 |
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WO |
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2009021216 |
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Feb 2009 |
|
WO |
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2013083876 |
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Jun 2013 |
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WO |
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2014029918 |
|
Feb 2014 |
|
WO |
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2014116150 |
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Jul 2014 |
|
WO |
|
Other References
Safety Data Sheet for Eastman(TM) Dilute Acetic Acid, 56%, 12
pages, 2016. cited by examiner .
Caicedo, Hector M., Luisa A. Dempere, and Wilfred Vermerris.
"Template-mediated synthesis and bio-functionalization of flexible
lignin-based nanotubes and nanowires." Nanotechnology 23.10 (2012):
105605. cited by examiner .
Search Report for FI20155728 dated May 16, 2016. cited by applicant
.
Finnish Patent and Registration Office, Office Action, dated May
16, 2016. cited by applicant .
Orbis Research, "Lignin Products Global Market Size, Sales Data
2017-2022 & Applications in Animal Feed Industry,"
https://www.reuters.com/brandfeatures/venture-capital/article?id=4789,
dated Apr. 20, 2017. cited by applicant .
Tomani, Per, "The Lignoboost Process," Cellulose Chemistry and
Technology, 44 (1-3), 53-58 (2010), dated Nov. 16, 2009. cited by
applicant .
Lamfeddal Kouisni, Peter Holt-Hindle, Kirsten Maki, Michael
Paleologou, "The Lignoforce System.TM.: A New Process or the
Production of High-Quality Lignin from Black Liquor," Journal of
Science & Technology for Forest Products and Processes: vol. 2,
No. 4, 2012. cited by applicant .
Michael A. Lake and John C. Blackburn, "SLRP.TM.--An Innovative
Lignin-Recovery Technology," Cellulose Chemistry and Technology, 48
(9-10), 799-804 (2014). cited by applicant.
|
Primary Examiner: Hill; Nicholas E
Attorney, Agent or Firm: Stiennon & Stiennon
Claims
We claim:
1. A method for producing solid lignin from lignin-rich starting
material, characterized by suspending the starting material in a
first medium, which is an aqueous solution of an inorganic acid
having a pH in the range of from 0 to 5, to form an aqueous acidic
suspension having a dry solid content of 10-25 weight percent;
heating the aqueous acidic suspension to a temperature in the range
of 120 to 180.degree. C. and allowing the suspension to form two
continuous phases, a phase comprising thermoplastic lignin and an
aqueous phase; separating the phase comprising thermoplastic lignin
from the aqueous phase; passing the separated phase comprising
thermoplastic lignin through a shape giving process into a second
medium, which is at a temperature lower than that of the
thermoplastic lignin phase and in which the phase comprising
thermoplastic lignin is essentially insoluble, whereby the lignin
solidifies in a form of granules when it is brought in contact with
the cooler second medium; and recovering the solid lignin formed in
the second medium; wherein the separated phase comprising
thermoplastic lignin is introduced to the second medium through one
or several nozzles and the second medium is water.
2. The method according to claim 1, wherein the first medium is an
aqueous solution of sulfuric acid, hydrochloric acid, nitric acid
or phosphoric acid.
3. The method according to claim 2, wherein the first medium is an
aqueous solution of sulfuric acid.
4. The method according to claim 1, wherein the pH of the first
medium is in the range of 0 to 4.
5. The method according to claim 1, wherein the suspension is
heated to a temperature in the range of 140 to 180.degree. C.
6. The method according to claim 1, wherein the phase comprising
thermoplastic lignin is separated from the aqueous phase by
gravity.
7. The method according to claim 1, comprising: subjecting the
separated phase comprising thermoplastic lignin to intermediate
processing before introducing it to a second medium.
8. The method according to claim 7, wherein the intermediate
processing is a purification process.
9. The method according to claim 7, wherein the intermediate
processing is a mixing process where additional material is mixed
with the separated phase comprising thermoplastic lignin.
10. The method according to claim 9, wherein the additional
material mixed with the separated phase comprising thermoplastic
lignin is a polymer or mixture of polymers other than lignin.
11. The method according to claim 1, comprising prior to suspending
the lignin-rich starting material in the first medium, slurrying
the starting material in an acidic aqueous medium at a temperature
lower than that of the first medium.
12. The method according to claim 1, comprising prior to suspending
the lignin-rich starting material in the first medium, slurrying
the starting material in an alkaline aqueous medium at temperature
lower than that of the first medium.
13. The method according to claim 1, comprising: adding a pH
lowering agent to a lignin containing liquid medium for
precipitating lignin; separating the precipitated lignin from the
remaining liquid phase of the lignin containing liquid medium; and
using the separated precipitated lignin as the starting material,
which is suspended in the first medium.
14. The method according to claim 13, wherein the lignin containing
liquid medium is alkaline spent pulping liquor.
15. The method according to claim 14, wherein the lignin containing
liquid medium is black liquor.
16. The method of claim 14, wherein the first medium is an aqueous
solution of sulfuric acid.
17. The method of claim 1 further comprising: suspending the
starting material in the first medium in a mixing tank, separating
the phase comprising thermoplastic lignin from the aqueous phase in
a phase separation unit, and recycling acidic aqueous phase from
the phase separation unit to at least one of: the mixing tank, and
to be used in pretreatment steps of lignin feedstock.
18. The method of claim 17, comprising: utilizing heat of the
recycled aqueous acidic phase in preheating the lignin-rich
starting material.
19. A method for producing solid lignin granules from lignin-rich
starting material, characterized by suspending alkaline spent
pulping liquor or black liquor in a first medium, which is an
aqueous solution of an inorganic acid having a pH in the range of
from 0 to 5, to form an aqueous acidic suspension having a dry
solid content of 10-25 weight percent; heating the aqueous acidic
suspension to a temperature in the range of 120 to 180.degree. C.
and allowing the suspension to form two continuous phases, a phase
comprising thermoplastic lignin and an aqueous phase; separating
the phase comprising thermoplastic lignin from the aqueous phase by
an acceleration selected from gravity and centripetal; and passing
the separated thermoplastic lignin phase through at least one
nozzle into water having a temperature lower than that of the phase
comprising thermoplastic lignin and in which the phase comprising
thermoplastic lignin is essentially insoluble, such that the phase
comprising thermoplastic lignin forms droplets which solidify in
the shape of granules with a selected size distribution controlled
by the at least one nozzle.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
This application claims priority on Finnish Application No.
20155728, Filed Oct. 13, 2015, the disclosure of which is
incorporated by reference herein.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED
RESEARCH AND DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing solid
lignin from a starting material containing lignin.
Lignin has been recognized for a long time as an underexploited
renewable resource available for mankind. Today lignin rich streams
available at pulp mills are used primarily in heat generation, i.e.
they are combusted in recovery boilers. Separation of lignin from
pulp mill spent liquor has not become popular mainly due to two
reasons: lack of technically feasible solutions for executing the
separation and lack of lignin-based value chains. Today, the global
trend of developing bio-based applications has made lignin
production attractive at a whole new level.
It is known to separate lignin from pulp mill black liquor using
the following stages in sequence:
precipitation of lignin by a first stage of the pulp mill black
liquor where the pH of the black liquor is lowered by adding a pH
lowering agent, preferably CO2
followed by a first dewatering stage while forming a first filter
cake,
suspending the first filter cake in a second stage using a second
acid or mixture of acids, wherein a lignin suspension is
obtained,
dewatering the lignin suspension by a second dewatering stage for
forming a second filter cake,
washing the second filter cake by adding a wash liquid to this
washing stage, and
dewatering the washed second filter cake obtaining a lignin
product, said dewatering being typically made in the last stage of
the wash apparatus.
Typically, the above described process is connected to the recovery
operations receiving black liquor from a digester of the pulp
mill.
These methods are known for example from international publication
WO 2006/031175 (corresponds to European patent EP 1794363 and U.S.
Pat. No. 8,486,224), and US Patent Application US 2010/0325947 A1.
The lignin product obtained by these methods can be used as fuel or
raw material for chemicals.
International publication WO 2009/021216 (corresponds to U.S. Pat.
No. 8,613,781) presents a method where a moist lignin mass (up to
85% water, normally 45-55%) already separated from black liquor is
heated to a "critical temperature" (76-93.degree. C.), which
induces a phase transition in the lignin. When the mass is
subsequently cooled, the lignin will be separated on the bottom,
leaving water as supernatant. According to another embodiment,
shown by FIG. 3 of the document, dilute black liquor (not
evaporated) is mixed with polymer coagulant agent and with heated
diluted phosphoric acid so that the temperature of the mixture
remains above 82.degree. C. and the pH is below 3.5, whereafter the
mixture is fed to a lignin separation tank, where the lignin is
separated upon cooling.
International publication WO2014/116150 presents a method where
lignin is first precipitated from black liquor with carbon dioxide,
and to the obtained lignin cake, sulphuric acid is added to form an
acidic slurry with a pH value in the range 1-3. The acidic slurry
is heated to the temperature in the range 100-120.degree. C. and
kept in the temperature range a sufficient time so that at least
60% of carbohydrates (hemicelluloses) in the lignin are hydrolyzed,
whereafter the slurry is cooled and purified lignin with low
carbohydrate content is separated from the cooled slurry by
filtration.
The process according to WO2014/116150 produces purified lignin,
which after further processing can be used in higher value
applications instead of using the lignin only as fuel because of
its purity, especially low carbohydrate content. There exists,
however, a need to control the physical solid state of the lignin
so that the lignin obtained is more easily processable and possibly
already in the form which is closer to its form in the final
application.
SUMMARY OF THE INVENTION
It is an aim of the present invention to present a novel process
using the lignin obtained from plant material for converting it to
more refined form.
The aim of the invention is to provide a method for processing
lignin separated from a lignin containing liquid medium, especially
spent liquors resulting from biomass fractionation, such as spent
liquor from alkaline cooking process of pulp, so that the lignin is
in a more refined form after the method.
It is especially an aim of the present invention to provide a
method which increases the value and possibilities of the lignin
for various uses in structural applications.
In order to achieve the aims presented above, the invention is
characterized by
suspending the starting material in a first medium, which is acidic
and aqueous, to form a aqueous acidic suspension;
heating the aqueous acidic suspension and allowing the suspension
to form two continuous phases, a thermoplastic lignin phase and an
aqueous phase;
separating the thermoplastic lignin phase from the aqueous
phase;
passing the separated thermoplastic lignin phase into a shape
giving process by introducing it to a second medium which is at a
temperature lower than that of the thermoplastic lignin phase and
in which the thermoplastic lignin phase is essentially insoluble;
and
recovering the solid lignin formed in the second medium.
Thus in the method, lignin-rich starting material in solid form,
which is originally separated from a spent liquor of a biomass
fractionation process, is suspended in an acidic aqueous solution
whose acidity is set high enough to keep the resulting acidic
aqueous suspension at pH of 1-5. The temperature of the suspension
is set high enough to induce the formation of two continuous and
separate phases: a thermoplastic (soft, viscous) lignin phase as a
result of softened and agglomerated lignin particles, and an
aqueous phase, where some lignin particles may remain suspended.
The phases can be separated by gravitation or centrifugation
because of their density differences. The separated thermoplastic
lignin phase is then introduced to a second medium which is at a
lower temperature than the continuous thermoplastic lignin phase.
The thermoplastic properties of the continuous lignin phase can be
used to give the lignin a desired solid shape by means of a
shape-giving structure, such as a nozzle or a plurality of nozzles,
through which it is fed to the second medium, and the lignin
solidifies in the given shape when it is brought in contact with a
cooler second medium. The lignin can be in the form of particles
with desired size distribution
The method involves the change of the physical state of the lignin,
starting from solid lignin particles of any kind in the starting
material, passing through the agglomeration (coalescing) of the
particles to the physical state of thermoplastic continuous phase,
and ending in the physical conversion of the thermoplastic phase to
a solid lignin product with targeted shape of the lignin. Due to
the shaping possibilities, the product can be for example in
granulated form or any other form which is easy to handle, contrary
to a dry lignin powder which is susceptible to dusting.
Because the lignin-rich starting material is suspended in an acidic
aqueous medium at an elevated temperature, the impurities, such as
metals and carbohydrates (hemicellulose residues from the original
plant biomass) in the lignin, are effectively removed from the
lignin and removed with the acidic aqueous phase.
Some preferred embodiments of the invention, related to the shape
giving processes and possible preprocessing steps are described
more closely in the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in more detail with reference to
the appended drawings, in which:
FIG. 1 shows a process flow chart of the method according to one
embodiment of the invention,
FIG. 2 shows a process flow chart of the method according to
another embodiment of the invention, and
FIG. 3 shows a process flow chart of the method according to a
third embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Origin of Lignin
The lignin rich starting material used in the method is obtained
from a biomass fractionation process, where lignin is a constituent
of plant biomass from which it becomes separated in the course of
the process. The biomass may contain residual lignin after the
process. A typical fractionation process is a process called
delignification, where lignin is separated from cellulose by
cooking the biomass with the help of chemicals and it is carried
over to spent liquor of the cooking chemicals, and it can be
sulphite, soda (including soda-anthraquinone), or kraft (sulphate)
delignification process. Thus, the spent liquor can be for example
black liquor from kraft (sulphate) cooking.
The lignin can come from other biomass fractionation processes as
well, where it is separated in course of the fractionation. One
possible source is the biomass fractionation process where
bioethanol is made from lignocellulosic biomass through hydrolysis
of cellulose to sugars and subsequent fermentation and
distillation. The hydrolysis of cellulose can be acidic or
enzymatic. This biomass fractionation process leaves a lignin-rich
residue which can be used as the lignin-rich starting material for
the present method. Thus, all fractionation processes of
lignocellulosic biomass where a lignin-rich fraction is produced
can serve as the source of lignin-rich starting material for the
present method.
It is intended throughout the present description that the
expression "lignin containing liquid medium" is any liquid, which
contains lignin in dissolved or dispersed form, especially any
spent liquor from a biomass fractionating process, especially
biomass fractionation in a chemical pulp mill. The origin of the
lignin is wood or other plant biomass such as straw that has been
digested in the pulp mill in a process called cooking to prepare
chemical pulp. The composition of the spent cooking liquor depends
on the cooking method. The spent liquor from kraft (sulphate)
cooking which is obtained after the separation of the pulp is
called black liquor and it contains dissolved and dispersed organic
wood material and residual alkali compounds. In the following
description, mainly black liquor is referred to as the lignin
containing liquid medium from which the lignin used as the starting
material can be separated. All lignin containing spent liquors from
alkaline cooking processes (which include soda cooking and
soda-anthraquinone cooking) can be used.
The composition of the lignin containing liquid medium and the form
of lignin therein is dependent on the preceding process and its
conditions where lignin has entered this liquid medium. The liquid
medium is preferably an aqueous medium, where lignin can exist as
solution, colloidal dispersion or slurry. For example it is known
that the lignin is either dissolved or dispersed in black liquor in
the colloidal form, depending on the pH of the black liquor and
lignin molecular weight. The colloidal dispersion is stabilized by
charged phenolic and carboxylic acid groups on the lignin (Marton,
J., On the structure of kraft lignin, Tappi, 47(11), 713-719
(1964)). In the precipitation of the lignin from the liquid medium,
lignin of such an increased particle size is created which can be
separated from the liquid medium by physical methods, especially by
filtration.
Production of Solid Lignin Through Treatment of Lignin-Rich
Starting Material
FIG. 1 shows, the general principle of the method as a
flowchart.
The process described purifies and agglomerates lignin precipitated
from alkaline spent pulping liquor (black liquor). The black liquor
feedstock may originate from chemical pulping of wood, annual,
biennial, or perennial plants using hydroxide, carbonate, or
sulfide salts or a combination of these as the active pulping
chemical.
Lignin (lignin salt) is separated from black liquor using known
methods. Preferably, lignin is precipitated by reducing the black
liquor pH to 8-10 by adding a pH lowering agent, and the
precipitate formed is separated from black liquor by filtration.
The lignin separated contains a substantial amount of impurities
both as black liquor carry over and as carbohydrate components
covalently attached in lignin macromolecules.
The lignin feedstock, precipitated alkaline lignin (arrow
"Precipitated lignin" in FIG. 1) is suspended in a first medium, an
acidic aqueous solution, in a mixing tank T. The acidity of the
solution is set high enough to keep the resulting suspension at pH
0-5, preferably 0-4, most preferably 2-4. The acid used may be
organic or inorganic. Suitable inorganic acids are for example
sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid.
The consistency of the lignin suspension is preferably 10-25 wt-%,
calculated as percentage ratio of oven dry lignin/(oven dry
lignin+liquid medium).
The suspension in the mixing tank T is heated to 120-180.degree.
C., preferably 120-160.degree. C. or 140-180.degree. C. The
suspension may be agitated or not. The conditions applied soften
the lignin particles and lead to their agglomeration. The
coalescence of lignin particles leads to a state where the original
suspension (solid particles in a continuous liquid phase) is mostly
converted into a system of two continuous phases: an aqueous liquid
phase and a thermoplastic (soft, viscous) lignin phase. Some lignin
may remain suspended in the aqueous phase. The upper and lower
limits of the temperature range and the optimum temperature to
which the lignin suspension is heated depends for example on the
type or origin of the lignin and the viscosity. When the
temperature is too low, there is no change in the physical state of
the lignin, and when the temperature is too high, there will be
changes in the chemical properties of the lignin, the lignin
becomes too sticky, and tends to adhere to the equipment used.
The term "suspending" and "suspension" does not exclude the
physical form where part of the lignin may also be in a dissolved
form.
The formation of the two continuous and separate phases takes place
in a phase separation unit, to which the heated and acidified
aqueous lignin suspension is introduced from the mixing tank.
The phase separation unit may be provided with heating to keep the
temperature of the system at a suitable value. When the system is
allowed to settle in the phase separation unit, the two phases form
independent continuous layers due to their different densities. The
continuous thermoplastic lignin phase, which is heavier, will be
settled on the bottom part of the phase separation unit, and the
aqueous acidic phase will remain on the top. Phase separation may
be allowed to occur by gravitation or it may be accelerated using
centrifugal processes. The settling time used may be for example 30
min. The two phases formed can be separated via decanting or
similar methods.
From the phase separation unit, the thermoplasticized lignin is
introduced to a second medium, where it is brought back to particle
form or to other solid shapes by cooling, which takes place by the
effect of the temperature of the second medium which is lower than
that of the thermoplastic lignin phase. In FIG. 1, the
thermoplasticized lignin is taken from the bottom of the phase
separation unit as a thermoplastic lignin stream, which is passed
to a low-temperature bath of the second medium in which the lignin
is immiscible (indicated "Low-temp granulation step"). The second
medium is water at a temperature below 100.degree. C. Solid lignin
particles or "granules" are formed in the cool medium by passing
lignin through a shape giving process in form of a nozzle or
several nozzles into the cool medium. Lignin is transformed into a
droplet form by the nozzle. A decreased temperature makes the
droplets harden, thus preventing re-coalescence. Instead of water,
air can also be used as the cool medium, and also other liquids and
gases may be used, provided that they are at a temperature which
solifidies the thermoplastic lignin after entry of the lignin in
the second medium.
The size properties of the resulting granules, e.g. average size
and size distribution, are controlled e.g. with the nozzle
arrangement. However, the shape giving process through which the
thermoplastic lignin phase passes before entering the cool second
medium can be used for giving any other shape to the objects of
lignin when the lignin solidifies in the medium, and this can be
achieved both with liquid and gaseous media as second media. It is
for example possible to make elongated objects, such as fiber-like
or filament-like objects by selection of nozzle diameter and flow
rate of the thermoplastic lignin stream to the second medium. By
choice of nozzle shape, other shapes are also obtainable, like
tubular objects or profiles. Extrusion or injection molding can
also be used for introducing the lignin into the second medium.
Thus, the introduction of the thermoplastic lignin to the second
medium through a shape-giving structure that determines the shape
of the lignin can be called a shape-giving process.
Next the solid lignin product is separated from the second medium
in a separation step. Because the size and shape of the objects
formed of solidified lignin can be controlled in the shape-giving
process, the separation can take place without filtration of the
lignin from liquid medium. For example the lignin granules formed
are large enough to facilitate easy de-watering (separation from
the surrounding aqueous phase) and handling in further processing,
if the second medium is water. Sedimentation, settling, draining,
centrifugation and cyclone separation are suitable solid-liquid
separation methods for the objects of solidified lignin. If the
second medium is air, the objects of solidified lignin can be
separated by cyclone from the stream of air or settled and gathered
from the stream of air by any suitable arrangement.
Furthermore, the lignin product formed is of high purity:
hemicellulose impurities covalently bonded or adsorbed on lignin
are effectively degraded under the hot acidic conditions applied
when the starting material is suspended in the first medium, and
practically all water soluble impurities, including the
hemicellulose degradation products, exit the process in the aqueous
side stream separated in the phase separation unit. If the second
medium is water, water soluble impurities such as metal salts,
which were formed by the effect of the acid used in the first
medium (such as Na2SO4 if sulphuric acid was used) can still be
washed from the solidified lignin to the surrounding aqueous phase.
If the second medium is air, the objects of solidified lignin can
be subjected to a washing step.
According to FIG. 1, various process streams can be recycled. The
aqueous' acidic phase (Acidic brine) from the phase separation unit
can be recycled, to the mixing tank to make the acidic aqueous
solution and/or to be used in pretreatment steps of the lignin
feedstock. Fresh acid (Make-up acid) is added to the mixing tank to
keep the pH at sufficient low level. After separating the lignin,
the second medium from the separation step can be recycled back to
the bath of second medium.
FIG. 2 shows an embodiment of the method which comprises a
preliminary slurrying step for the lignin feedstock before it is
brought in contact with the first medium. The alkaline lignin
filter cake obtained from the separation of lignin from the
alkaline spent pulping liquor is slurried in a medium, which is
acidic and aqueous, but has a lower temperature than that of the
first medium (acidic preliminary slurrying). The operation is
performed in a preliminary mixing tank PT. The temperature of the
medium where the alkaline lignin is slurried is below 100.degree.
C. The aqueous acidic phase from the phase separation unit can be
recycled to this preliminary slurrying step to form the preliminary
slurrying medium. In this preliminary slurrying step, some
purification of the lignin may already take place. The heat of the
recycled aqueous acidic phase (Acidic brine) can be utilized in
preheating the lignin feedstock before the lignin is introduced to
the mixing tank (shown by heat exchanger). Alternatively, make-up
acid added to the mixing tank can be used also for the preparation
of the preliminary slurrying medium. The pH of the slurry can be
adjusted to be the same as the pH of suspension in the first medium
already at this stage, if fresh acid is added to this stage (arrow
"alternative"). If the slurry is made by only recycling the aqueous
acidic phase from the first medium, the pH will higher due to the
alkalinity of the filter cake.
FIG. 3 shows another embodiment of the method which comprises a
preliminary slurrying step for the lignin feedstock before it is
brought in contact with the first medium. The alkaline lignin
filter cake obtained from the separation of lignin from the
alkaline spent pulping liquor is preliminarily slurried in a
preliminary mixing tank PT. The slurry is alkaline and aqueous due
to the alkalinity of the cake (alkaline preliminary slurrying), but
has a lower temperature than that of the first medium. Water can be
added if needed to make a pumpable slurry. The temperature of the
alkaline lignin slurry is below 100.degree. C., preferably not
higher than 80.degree. C. The alkaline preliminary slurrying has
less emissions of H2S from the lignin compared with the acidic
preliminary slurrying in case the lignin is from kraft (sulphate)
cooking.
The embodiments of FIG. 2 and FIG. 3 help to make a pumpable slurry
which can be fed from the preliminary mixing tank PT to the mixing
tank T where the suspension is at the higher temperature. It is
also easier to add lignin-rich starting material to an atmospheric
tank at a temperature below 100.degree. C. to make a suspension
than to the mixing tank, which is a pressurized reaction tank
because the temperature inside the tank is well above 100.degree.
C. In FIGS. 2 and 3, the pump in the conduit between the
preliminary mixing tank PT and the mixing tank is designated P, and
the heat exchanger for preheating the pumped lignin slurry in the
conduit with the hot acidic aqueous phase from the phase separation
unit is designated H.
The method also offers a possibility to include additional
materials to the solid lignin product during various steps of the
method, especially to the thermoplastic continuous phase of the
lignin. The additional material mixed to the separated
thermoplastic lignin phase can be a polymer or mixture of polymers
other than lignin, which include synthetic polymers and cellulose,
to modify the material properties of the product. Substances adding
some functional properties to the lignin, such as coupling agents
and activators, can also be added. However, the amount of
additional materials should be below 50 wt-% of the total dry
weight of the solid lignin product.
The method also offers a possibility to subject the thermoplastic
lignin, before introducing it to the shape giving process and
second medium, to intermediate processing which is purification.
Water and/or metals that may exist in the lignin can be further
removed in this step from the thermoplastic phase of lignin.
The method according to the invention can be integrated in a
chemical pulp mill where alkaline cooking process is used for the
delignification of pulp. Alkaline lignin used as the lignin-rich
starting material of the method can be precipitated from the
alkaline spent liquors of the cooking process. For example black
liquor can be taken at any point between the digester and the
recovery boiler, preferably from the evaporation stage where it has
not yet reached the final dry solids content where it is burnt in
the boiler. The separation of lignin takes place by adding pH
lowering agent, for example CO2, to the black liquor, and the
lignin precipitated at the lowered pH is separated from the
obtained slurry for example in a filter press. The lignin cake so
obtained can be used as the lignin-rich starting material of the
method.
The method can also be integrated in a bioethanol-production plant
which uses lignocellulosic raw material and produces a lignin-rich
residue as a side product.
However, the method can be also performed in a separate
manufacturing plant to which the lignin-rich starting material
(such as alkaline lignin separated from alkaline spent liquor by
precipitation or lignin-rich residue of bioethanol production, as
explained above) is transported.
The applicability of the process stages described above in
connection with embodiments of FIGS. 1, 2 and 3 is not dependent on
the source of the lignin-rich starting material and the separation
of this raw material in the process where this raw material is
obtained. The lignin-rich starting material may be separated from a
spent liquor of a biomass fractionation process, such as from
alkaline spent pulping liquor, it may be in the form of lignin-rich
residue from bioethanol production, or it may be originally from
any biomass fractionation process that produces lignin-rich
starting material that can be suspended in the first acidic aqueous
medium or re-slurried in the mixing tank (FIGS. 2 and 3). It is
also possible that some mechanical processing such as milling is
needed before the lignin-rich starting material can be supplied to
the process.
Many variations of the present invention will suggest themselves to
those skilled in the art in light of the above detailed
description. Such obvious variations are within the full intended
scope of the appended claims.
* * * * *
References